Sudsplanter has completed a multi-site sustainable drainage project across seven schools in the London Borough of Merton, helping to manage surface water runoff and reduce the risk of localised flooding.
Identified by the council as being at high risk of surface water flooding through risk mapping, the schools had experienced recurring issues including water pooling in playgrounds, disrupting outdoor activities. In some cases, flooding also affected classrooms and learning environments.
Part-funded through the SuDS in Schools programme and supported by the Department for Education, the project aligns with the “capture” principle of the London Surface Water Strategy.
Sudsplanter designs and manufactures modular rain gardens known as SuDSPlanters. The systems divert roof runoff from downpipes into planted features rather than allowing it to enter the sewer network immediately.
Each SuDSPlanter unit is designed as a layered system combining attenuation, filtration and storage. Rainwater is captured within a specially formulated soil mix and underlying reservoir, where it is temporarily stored before being released at a controlled rate.
The process is designed to mimic natural drainage, reducing peak flows entering the sewer system during storm events and helping to mitigate the risk of sewer surcharge and localised surface water flooding.
Following site selection, Sudsplanter’s surface water management specialists visited each school alongside a council officer to identify locations where the installations could provide the greatest benefit. The assessment considered existing drainage systems, roofs and downpipes.
As the project was required to provide a defined level of flood protection, Sudsplanter used modelling tools to calculate the projected storage and attenuation capacity. This was used to ensure the scheme met Department for Education key performance indicators covering areas including design, installation and maintenance.
The calculations showed that installing 29 SuDSPlanter units across the seven schools would:
• Reduce peak discharge to the sewer per downpipe by between 81% and 95%;
• Withhold 24.49 cubic m of rainwater upstream of the sewer network, releasing it later at low rates; and
• Provide a total roof rainwater attenuation volume of 14.7 cubic m.
Between three and six bespoke SuDSPlanter units were installed at each school, with plant varieties selected by horticulturalists according to local conditions and site aspect.
Sudsplanter’s education specialists also ran sessions with pupils covering the water cycle, sustainable drainage systems (SuDS), and how to care for the plants and newly created habitats.
Long-term maintenance of the systems will be led by each school, supporting local ownership and day-to-day care. The council will carry out annual check-ins to gather updates on performance.
“Surface water flooding is one of the primary sources of flood risk in Merton, occurring during heavy rain when the ground is unable to absorb the water and the drainage system is overwhelmed,” said Bethan McGregor, climate projects officer at London Borough of Merton.
“That’s why we were pleased to secure SuDS in Schools funding for seven sites that had been impacted by surface water flooding. Sustainable drainage systems are an important feature in our local flood strategies — and schools offer unique opportunities to address risk while creating educational and biodiversity benefits,” McGregor explained. “The SuDSPlanters have delivered tangible benefits. In just one of many examples, one school reported that its playground, which usually floods after rain, has not flooded since the planters were installed in Dec.”
“By installing SuDSPlanter units, Merton Council has provided these schools with an ongoing engagement resource that provides water quality benefits, flood protection, biodiversity enhancements, education tools and health and wellbeing benefits, to name but a few,” said Lorna Davis, director at Sudsplanter. “The project was part-funded by the Department for Education — we would encourage local authorities in areas impacted by flooding to explore similar funding opportunities.”
